In recent years, there have been developed fuel cells wherein: an anode on which platinum is carried and a cathode are arranged to sandwich a solid polymer electrolytic membrane, thereby forming an electrode/solid electrolyte/electrode structure; the electrode/solid electrolytic membrane/electrode structure is sandwiched between a pair of current collectors each having a channel formed in the inside face thereof; and a fuel and oxygen (or air) are supplied into the two channels, respectively, thereby generating electricity. There has also been made research on the matter that such fuel cells are laminated or two-dimensionally connected so as to improve the voltage or power thereof and the resultant is integrated into a system.
Such fuel cells are clean and have high efficiency, and further are not required to be electrically charged for a long period as performed in conventional secondary cells. From the viewpoint of a feature that substantially continuous use thereof can be attained when fuel is continuously supplied thereto, attention is paid to the use thereof for various purposes, in particular, power sources for electric automobiles, dispersed power sources for household, power sources for portable instruments, and others.
Meanwhile, as a fuel supplied to the anode, the following has been typically investigated: a gas fuel such as pure hydrogen, or hydrogen generated from a fuel such as alcohol or hydrocarbon by use of a reforming catalyst, which may be referred to as reformed hydrogen hereinafter; a mixed liquid fuel, such as water and methanol, dimethyl ether, ethylene glycol or polyhydric alcohol; or the like. However, problems remain. That is, fuel cells using liquid fuel give a low power and fuel cells using gas fuel output a low volume energy density from the viewpoint of storage and transportation thereof.
Thus, suggested is a method of mounting not only a fuel cell itself but also a reforming device onto a system, and generating electricity at the same time of generating reformed hydrogen from a liquid fuel. However, carbon monoxide is generated in the reforming-reaction and it remains in the reformed hydrogen so as to cause a problem that the carbon monoxide poisons the platinum catalyst to make the power of the fuel cell low. Against this, there is a method of adding a device for removing carbon monoxide to the reforming device. However, according to such a method, the whole of the system becomes large-sized; therefore, this matter becomes a problem against use for portable instruments or automobiles, in which a usable space is limited. Thus, in the present circumstances, the content of carbon monoxide cannot be decreased to a level such that the carbon monoxide has no effect of poisoning.
Thus, as another method, various platinum alloy catalysts, a typical example of which is an alloy of platinum and ruthenium, are suggested as electrode catalysts which are less poisoned than platinum. However, advantageous effects thereof have not yet been sufficiently obtained. Furthermore, it is suggested that carbon monoxide in fuel gas for fuel cells is selectively oxidized so as to decrease the concentration of carbon monoxide in the fuel gas (Japanese Patent Application National Publication No. 2003-519067). However, this is not a method for restraining the electrode catalyst from being poisoned with carbon monoxide.
The present invention has been made in order to solve the above-mentioned problems involved in the prior art solid polymer fuel cells each of which has an anode on which platinum or a platinum alloy is carried as an electrode catalyst wherein reformed hydrogen is supplied as fuel into the anode. Therefore, it is an object of the invention to provide a solid polymer fuel cell making it possible to restrain its electrode catalyst from being poisoned with carbon monoxide contained in reformed hydrogen thereby to output a high power.